| 2023 Hardiness Zone: | Zone 6b: -5°F to 0°F |
| 2012 Hardiness Zone: | Zone 6a: -10°F to -5°F Zone 6b: -5°F to 0°F |
| 1990 Hardiness Zone: | Zone 6a: -10F to -5F |
| Average First Frost Date: | Oct. 11 - Oct. 20 |
| Average Last Frost Date: | Apr. 21 - Apr. 30 |
| Koppen-Geiger Climate Zone: | Dfa - Humid Continental Hot Summers |
| Ecoregion: | 72j - Southern Illinoian Till Plain |
| Heat Zone Days: | 61 - 90 days Over 86°F |
Annual Climate Data for ZIP Code 62837 - Fairfield, IL | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 20 | 24 | 34 | 43 | 53 | 62 | 66 | 63 | 56 | 44 | 35 | 25 | 44 |
| Avg Max Temp (°F) | 37 | 44 | 55 | 66 | 76 | 85 | 88 | 87 | 80 | 69 | 54 | 42 | 65 |
| Avg Precip (In.) | 2.73 | 2.68 | 4.4 | 4.67 | 4.72 | 4.13 | 3.81 | 3.27 | 2.96 | 3.23 | 4.27 | 3.47 | 44.36 |